Scr. XXX. EDUCTION OF MAGNETISM. 307 



quickly on the removal of the magnet, whereas the 

 steel is impressed with a lasting polarity. 



A certain time is requisite for the induction of mag- 

 netism, and it may be accelerated by anything that 

 excites a vibratory motion in the particles of the steel, 

 such as the smart stroke of the hammer, or heat suc- 

 ceeded by sudden cold. A steel bar may be converted 

 into a magnet by the transmission of an electric discharge 

 through it; and as its efficacy is the same in whatever 

 direction the electricity passes, the magnetism arises 

 from its mechanical operation exciting a vibration among 

 the particles of steel. It has been observed that the 

 particles of iron easily resume their neutral state after 

 induction, but that those of steel resist the restoration 

 of magnetic equilibrium, or a return to the neutral state ; 

 it is therefore evident, that any cause which removes 

 or diminishes the resistance of the particles will tend to 

 destroy the magnetism of the steel ; consequently, the 

 same mechanical means which develop magnetism will 

 also destroy it. On that account a steel bar may lose 

 its magnetism by any mechanical concussion, such as by 

 falling on a hard substance, a blow with a hammer, and 

 heating to redness, which reduces the steel to a state of 

 softness. The circumstances which determine whether 

 it shall gain or lose, are its position with respect to the 

 magnetic equator, and the higher or lower intensity of 

 its previous magnetic state. 



Polarity of one kind only cannot exist in any portion 

 of iron or steel ; in whatever manner the intensities of 

 the two kinds of polarity may be diffused through a mag- 

 net, they exactly balance or compensate one another. 

 The northern polarity is confined to one-half of a mag- 

 net, and the southern to the other, and they are gener- 

 ally concentrated in or near the extremities of the bar. 

 When a magnet is broken across its middle, each frag- 

 ment is at once converted into a perfect magnet ; the 

 part which originally had a north pole acquires a south 

 pole at the fractured end ; the part that originally had a 

 south pole gets a north pole ; and as far as mechanical 

 division can be carried, it is found that each fragment, 

 however small, is a perfect magnet. 



A comparison of the number of vibrations accomplished 



